摘要:

Soybean (Glycine max[L.] Merr. cv. Essex) was grown in an unshaded greenhouse under three levels of biologically effective ultraviolet‐B (UV‐BBE) radiation (effective daily dose: 0, 11.5 and 13.6 kJ m–2) for 91 days. Plants were harvested at regular intervals beginning 10 days after germination until reproductive maturity. Mathematical growth analysis revealed that the effects of UV‐B radiation varied with plant growth stage. The transition period between vegetative and reproductive growth was the most sensitive to UV‐B radiation. Intermediate levels of UV‐B had deleterious effects on plant height, leaf area, and total plant dry weight at late vegetative and reproductive stages of development. Specific leaf weight increased during vegetative growth but was unaffected by UV‐B during reproductive growth stages. Relative growth, net assimilation, and stem elongation rates were decreased by UV‐B radiation during vegetative and early reproductive growth stages. Variation in plant responses may be due in part to changes in microclimate within the plant canopy or to differences in repair or protection mechanisms at differing developmental stages.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08706.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Mature needles and elongating current year's needles ofPinus strobusgrowing in Massachusetts andP. brutiagrowing in Israel were collected monthly or bimonthly for seasonal analysis of leaf cambial activity. Mature needles produced secondary phloem but no xylem, and, regardless of the season, had a cambial zone from 2 to 3 cell layers wide. In the current year's needles maturation was basipetal and the procambium differentiated into primary xylem, primary phloem, and the phloem‐producing vascular cambium before needle maturity. One‐ and 2‐year‐old needles ofPinus strobusproduced slightly over 4 cell layers of phloem between April 15 and September 1 of 1983, with a peak production rate of about 2 cell layers per month in May and early June. One‐year‐old needles ofP. brutiaproduced about 6 phloem cell layers in 1983, with phloem being produced throughout the year except in midsummer. This was contrasted by fall and winter dormancy in needles ofP. strobus.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08707.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The relative importance of prezygotic mechanisms of gametophytic competition and selection are often unclear due to an absence of observations on the gynoecium and pollen tube growth in vivo. We used LM, SEM, and TEM to study the structure of the gynoecium and the path of pollen tube growth inRaphanus raphanistrum, a sporophytically self‐incompatible annual.Wild radish has a papillate stigma and a solid style. A septum, which is characteristic of cruciferous gynoecia, is present in the ovary. After germination on the stigma, pollen tubes grow in the secretion of the transmitting tract of the style. The stylar secretion stains positive for acidic polysaccharides and insoluble carbohydrates, and negative for lipids and protein. In the ovary, the transmitting tissue is contained inside the septum. The secretion in the ovary stains positive only for acidic polysaccharides. Pollen tubes travel inside the septum as they enter the ovary and must exit to the surface of this tissue before ovule fertilization can occur. Pollen tube growth on the septum tracks the intercellular junctions of the septum epidermis where the secretion leaks out through a torn cuticle. Tubes must grow across the obturator before reaching the micropyle of an ovule. The temporal pattern with which tubes growing into the ovary exit the septum can contribute to the previously observed nonrandom patterns of fertilization (Hill and Lord, 1986).

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08708.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Because CO2uptake by cacti can be limited by low levels of photosynthetically active radiation (PAR) and because plant form affects PAR interception, various cactus forms were studied using a computer model, field measurements, and laboratory phototropic studies. Model predictions indicated that CO2uptake by individual stems at an equinox was greatest when the stems were vertical, but at the summer and the winter solstice CO2uptake was greatest for stems tilted 30° away from the equator. Stem tilting depended on form and taxonomic group; four barrel cacti inFerocactusand inCopiapoaand four cylindropuntias inOpuntiatilted toward a horizontal light beam by an average of 18°, 48°, and 52°, respectively, after growth periods of 1 to 4 yr. In contrast, three columnar species showed no significant phototropic response, perhaps because structural stability requires their massive stems to be erect. Field plants of the dense, multiple‐stemmed shrubOpuntia echinocarpahad stems which tended to radiate outward from the plant base, and, although this would not influence the total PAR intercepted, it would result in a more uniform PAR distribution and hence higher CO2uptake. ForO. echinocarpaand the even denser, mound‐formingEchinocereus engelmannii, PAR and chlorophyll decreased approximately exponentially with depth into the canopy. The canopies ofO. echinocarpaand other cylindropuntias did not extend to the ground; in certain species, such truncation apparently resulted from a combination of very low PAR levels just below the lower canopy edge and the light‐dependent growth responses of individual stems. In addition, although the canopy surfaces ofO. echinocarpaandO. acanthocarpatilted toward the equator by about 30°, the canopies of other cylindropuntias tilted less or not at all; the computer model predicted that a 30° tilt would decrease interstem shading, increase daily PAR, and increase nocturnal CO2uptake by as much as 54, 26, and 24%, respectively. Not only can the shape of cacti be affected by PAR, but also shape influences PAR interception and hence CO2uptake.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08709.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

We launched imbibed seeds ofZea maysinto outer space aboard the space shuttleColumbiato determine the influence of microgravity on cellular differentiation in root caps. The influence of microgravity varied with different stages of cellular differentiation. Overall, microgravity tended to 1) increase the relative volumes of hyaloplasm and lipid bodies, 2) decrease the relative volumes of plastids, mitochondria, dictyosomes, and the vacuome, and 3) exert no influence on the relative volume of nuclei in cells comprising the root cap. The reduced allocation of dictyosomal volume in peripheral cells of flight‐grown seedlings correlated positively with their secretion of significantly less mucilage than peripheral cells of Earth‐grown seedlings. These results indicate that 1) microgravity alters the patterns of cellular differentiation and structures of all cell types comprising the root cap, and 2) the influence of microgravity on cellular differentiation in root caps ofZea maysis organelle specific.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08710.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The babassu palm (Orbignya phalerata) is an important source of oil and charcoal in Brazil. In some areas it grows in association withO. eichleri, and where their distribution is sympatric, a third palm is found. This taxon was described by Bondar in 1954 asO. teixeirana.As a result of intense fieldwork and subsequent morphological and anatomical studies, we conclude thatO. teixeiranais a hybrid betweenO. phalerataandO. eichleriand propose a change in its status to reflect this new understanding of its origin.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08711.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

The biomechanical relationship between the ability of a plant organ to resist bending and the extent to which tissues are hydrated is illustrated for the cylindrical leaves of chive (Allium schoenoprasnumvar.schoenoprasnumL.). The flexural rigidity (EI), which measures the ability to resist bending, is maximum when leaves are fully turgid and decreases monotonically as a function of water potential (r2= 0.99). Dehydration results in a reduction in the elastic modulus (E) of leaves. Reductions in E are correlated with geometric distortion in the transverse geometry of leaves which influences their second moment of inertia (I). The traditional theory of elastic stability (developed on the basis of the mechanical behavior of nonbiological systems) is shown to be inadequate to distinguish the behavior of E as plant organs geometrically distort during dehydration. This inadequacy results from the violation of a principal assumption made by the theory (= uniform cross‐sectional geometry). A derivation is presented that accommodates the localized geometric distortions in cylindrical plant organs and permits a valid estimate of reductions in E as tissues dehydrate. Based on this derivation, the Young's modulus of chive leaves just before mechanical failure due to buckling is shown to be less than 50% of that calculated for fully turgid leaves.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08712.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Solanum candidumof tropical America is very similar toS. lasiocarpumof southeastern Asia andS. sessiliflorum, a wild and domesticated plant of the Amazon basin, is very similar toS. repandum, a weed and domesticated plant of Oceania. Artificial hybrids betweenS. candidumandS. lasiocarpumare fertile, and it is postulated thatS. lasiocarpumresulted from a Spanish introduction ofS. candidumto Asia. Hybrids betweenS. repandumandS. sessiliflorumshow considerable reduction in fertility and abnormalities at meiosis, whereas hybrids of bothS. candidumandS. lasiocarpumwithS. repandumare fertile. It is concluded that it is likely thatS. repandumdid not arise fromS. sessiliflorumbut fromS. lasiocarpumorS. candidum.This would mean that the similarity ofS. repandumtoS. sessiliflorumresults from convergence.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08713.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Spinacia oleraceavar. Americana was hydroponically grown across an experimental salinity gradient ranging from 0.0 to 6.0 grams NaCl/liter nutrient medium. Twenty male, 20 female, and 20 monoecious plants were randomly harvested from each treatment where possible. Root biomass (RTA), biomass allocated to leaves and stems (VA), and reproductive biomass (RA) were determined. Male, female, and monoecious plants were shown to have significantly different patterns of RTA, VA, and RA. Moreover, the treatments influenced allocation patterns of the sexes differently, i.e., a partial niche separation was observed among the sexes along the gradient with respect to RTA, VA, and RA. Additionaly, the sexes expressed different trade‐offs between allocation of resources to the different tissues; most notably, under high salinity, RTA, and RA were strongly negatively correlated in females, but positively correlated in male and monoecious plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08714.x

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Inflorescences ofTripsacum dactyloides(L.) L. (Andropogoneae) are characterized by single female spikelets at one to several basal nodes and paired male spikelets at several nodes above them on each raceme. Female spikelets are one‐flowered and male spikelets are two‐flowered. A sex form variant was found in a wild population in north central Kansas and classified asT. dactyloides(L.) L. formaprolificumDayton et Dewald. The variant of this native distant relative of maize (Zea maysL. spp. mays) differs from the normal form by having both pistillate and perfect rather than staminate spikelets in the terminal (tassel) portion of the inflorescence and by having two functional pistillate florets in the basal spikelets instead of one. A recessive major gene at a single locus regulates the change of the inflorescence from monoecious to gynomonoecious.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1987.tb08715.x

出版商:Wiley    

年代:1987

数据来源: WILEY